Talk:Cyclobutadiene

Geometry
Cyclobutadiene cannot be square, due to the Jahn-Teller effect (a rare example of the Jahn-Teller effect in organic chemistry). The less-symmetrical rectangular geometry will always be more stable. Physchim62 16:42, 16 Jun 2005 (UTC)


 * Interesting...I have not thought of the Jahn-Teller effect here. The square is predicted by simple Huckel theory though, so I added that to the article. I also added the fact that it was with low temperature infrared studies which confirmed the rectangular structure. --HappyCamper 01:46, 24 July 2006 (UTC)

Unstable with respect to?
The article was written from what I thought was confusing perspective that cyclobutadiene is "unstable", "explained" with respect to Huckel rule, then a fair bit of discussion of excited states, etc. So I rewrote the article bearing in mind the old question, "unstable with respect to what?" If it is unstable with respect to dimers (never really explained in detail), then one "merely" installs bulky groups or employs site isolation methods.--Smokefoot (talk) 13:06, 25 February 2018 (UTC)
 * I think "unstable" was just used with the simplistic meaning of "disappeared before it could be isolated". However I agree that it is a good idea to be more specific if more details are available. I do have a few comments on the new version:
 * Intro: "cyclobutadiene alone is quite stable". What is meant by "alone"? This phrase seems to contradict the section on Trapping.
 * Intro: "the species can be observed by matrix isolation techniques". I would add "at temperatures below 35 K". Otherwise readers will have a natural tendency to assume it means at ordinary T.
 * Structure and reactivity: consistent with 2 dideutero stereoisomers. Have these isomers been observed?
 * Structure and reactivity: last sentence would be clearer as "This distortion indicates that the pi electrons are localized, in agreement with Hückel's rule which predicts that a pi system of 4 electrons is not aromatic."
 * Trapping: "even at T above 35K" should read "at T above 35K", since compound does not dimerize below 35K
 * Trapping: what is a hemicarciplex?? We had a link to "carciplex", but what does the "hemi" mean"?
 * And finally why suppress the experimental geometry of the tetra(t-butyl) derivative? It is probably our best indication of the cyclobutadiene geometry.

Dirac66 (talk) 02:49, 27 February 2018 (UTC)